JPS6297243A - Electrolytic ionization ion source - Google Patents

Abstract

PURPOSE:To make the needle surface chemically stable and to take out a stable ion beam by forming a needle in an electrolytic ionization type ion source with a tungsten carbide layer being provided on the surface of a tungsten needle. CONSTITUTION:A needle 14 in an electrolytic ionization type ion source is formed by providing a tungsten carbide layer 15 on the surface of a tungsten needle. Then it is placed in a reservoir 12 together with material to be ionized thereafter heated through a heating means 13 to moisten the surface of the needle 14 with a fused material 11. Thus, an ion beam 17 is taken out by means of a take-out electrode 16. the surface of th needle 14 is chemically stabilized by means of the tungsten carbide layer 15, thus preventing reaction with the needle 14 even when employing a chemically active material such as boron as the ionizing material. Consequently, the ion beam can be taken out stably for long time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrolytic ionization type ion source that generates an ion beam. This type of electrolytic ionization type ion source is used, for example, in processing semiconductors.

[Prior Art] By scanning an ion beam narrowly focused to about 0.1 μm using a deflector, it is possible to directly perform etching or ion implantation of a semiconductor substrate without using a mask or resist. For this purpose, an electrolytic ionization type ion source with high brightness and small source size is used.

FIG. 3 is a diagram showing an example of such an electrolytic ionization type ion source. This electrolytic ionization type ion source has R, Clamp
Nuclear 1 n5true by itt et al.
+entsand Meth*ds 149th Wp, 73
9-742 (1978).

Referring to FIG. 3, the electrolytic ionization type ion source includes a reservoir 32 in which a substance to be ionized 31 is stored, a needle 34 made of tungsten, a heating heater 33, and an ion beam extraction electrode 35. Be prepared.

When the substance 31 to be ionized is placed in the reservoir 32 and heated by the heater 33, the substance 31 to be ionized becomes molten and wets the surface of the tungsten needle 34. This molten material then flows to the tip of the tungsten needle 34. Then, when a negative voltage of 4 to 10 KV is applied to the ion beam extraction electrode 35 with respect to the needle 34, an electric field is concentrated at the tip of the needle 34, and the molten substance 31 at the tip of the needle 34 is transferred to the ion beam 34 by field emission. and is released.

The type of ion source shown has a very small source size and a very high Pi4 degree, making it possible to focus the ion beam to a diameter of 0.1μ or more using focusing optics. It is expected to be used in semiconductor device manufacturing.

[Problems to be Solved by the Invention] However, the illustrated l11w1i mold release 1' on source had the following problems. That is, needle 3
As the material 4, tungsten having a high melting point is generally used. However, when the substance 31 to be ionized is a highly active substance, for example, when boron, which is widely used as a P-type impurity in silicon semiconductor devices, is adopted as the substance 31 to be ionized. In this case, boron reacts with tungsten, which is the material of the needle 34, under the height 1, changing the shape of the tip of the needle 34. Therefore, it is not possible to obtain a stable ion beam by using such a highly active substance.

This invention was made to solve these problems, and its purpose is to provide an electrolytic ionization type ion source that can extract a stable ion beam even from highly active substances. That's true.

[Measures for solving the problem e] The electrolytic ionization type ion source according to the present invention has the following features.

83 A tungsten needle b having a tungsten carbide layer formed on its surface, a reservoir C6 that stores therein a substance to be ionized in a molten state and is capable of supplying the substance to be ionized to the tip of the tungsten needle. Heating means d for heating the tungsten needle and the reservoir; #i An ion beam extraction electrode for applying a positive potential of several KV to the tip of the tungsten needle [Function] A tungsten carbide layer is formed on the surface of the tungsten needle. This makes the surface of the tungsten needle chemically stable.

[Example] FIG. 1 is a schematic sectional view showing an example of the present invention. The illustrated electrolytic ionization type ion source includes a reservoir 12 for storing therein a substance 11 to be ionized, a heating means 13 such as a heater, a needle 14 made of tungsten, and an ion beam extraction N pole 16. A tungsten carbide layer 15 is formed on the surface of the tungsten needle 14 .

The substance to be ionized w11 is placed in the reservoir 12, and the tungsten needle 14 and the reservoir 12 are heated by the heating means 13. Then, the substance 11 to be ionized melts, wets the surface of the tungsten needle 14, and flows to the tip of the needle 14. Since the surface of the tungsten needle 14 is covered with chemically stable tungsten carbide m 15, even if the substance 11 to be ionized is a chemically active substance such as boron, the active substance There is no such thing as reacting with tungsten. Note that the reservoir 12 is also preferably made of a chemically stable material such as ceramic. If such a material is used, the reservoir 12 will not react with the substance 11 to be ionized.

A tungsten needle 1 is attached to the ion beam extraction electrode 16.
When a negative voltage of 4 to 10 KV is applied to the needle 14, the ion beam 17 is emitted from the tip of the needle 14.

As mentioned above, tungsten carbide 1115 is formed on the surface of the tungsten needle 14, but this J
: An example of a method for manufacturing eel needles will be described below.

FIG. 2 is a diagram sequentially showing the manufacturing process of a needle used in the iEN'l release ion source. First, <a>
As shown in , Tashidasten wires 21 having diameters varying from 0.1 to 0.5111 m are prepared. Next, as shown in (b), the Ja of the tungsten wire 21 is sharpened by electrolytic etching, for example, in potassium hydroxide. Reference numeral 22 denotes a sharpened tip as shown in A, and the tip has a radius of 5 tim or less. Next, as shown in CC), a carbon film 23 is applied to the surface of the tungsten wire 21 by a vacuum cleaner method.
form. Next, as shown in (d), carbon M
The tungsten layer 21 on which the film 23 is formed is
By heat-treating at about 1000° C. in a nitrogen atmosphere, the surface of the tungsten wire 21 is made into tungsten carbide 1i! Set it to 324.

In the embodiment shown in FIG. 1, ceramic is used as the material for the reservoir 12, but the reservoir 12 may be made of other materials. Examples of the material include carbon, tungsten with a tungsten carbide layer formed on the surface, or metal carbide. 1. That is, as the material for forming the reservoir 12, any chemically stable substance may be used.

[Effects of the Invention] As described above, according to the present invention, since the tungsten carbide layer is formed on the surface of the tungsten needle,
The surface of the tungsten needle becomes chemically stable. Therefore, even if a chemically active substance such as boron is used as the substance to be ionized, the active substance will not react with the tungsten needle, and as a result, a stable ion beam cannot be extracted for a long time. It becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view showing an embodiment of the present invention. FIG. 2 is a diagram sequentially showing an example of the manufacturing process of the tungsten needle used in the present invention. Figure 3 is a schematic cross-sectional view of a conventional electrolytic ionization type ion source.
be. In the figure, 11 is a substance to be ionized, 12 is a reservoir, 13 is a heating means, 14 is a tungsten needle, 1
5 is a tungsten carbide layer, 16 is an ion beam extraction electrode, and 17 is an ion beam.

Claims (5)

[Claims] (1) A tungsten needle with a tungsten carbide layer formed on its surface, a molten substance to be ionized stored inside, and the substance to be ionized to be supplied to the tip of the tungsten needle. An electrolytic ionization type ion source comprising: a reservoir; a heating means for heating the tungsten needle and the reservoir; and an ion beam extraction electrode for applying a positive potential of several KV to the tip of the tungsten needle. (2) The electrolytic ionization type ion source according to claim 1, wherein the material of the reservoir is ceramic. (3) The electrolytic ionization type ion source according to claim 1, wherein the material of the reservoir is carbon. (4) The material of the reservoir is tungsten with a tungsten carbide layer formed on the surface, claim 1.
The electrolytic ionization type ion source described in . (5) The electrolytic ionization type ion source according to claim 1, wherein the material of the reservoir is a metal carbide.